1. Field of the Invention
The present invention relates to a microwave oven, and more particularly to a food amount detector capable of automatically detecting the amount of food placed in the microwave oven, and to the microwave oven employing a food amount detector and a control method thereof.
2. Description of the Prior Art
Generally, a microwave oven heats/cooks the food by microwave. Such a microwave oven comprises a high voltage transformer and a magnetron. The high voltage transformer transforms common voltage (220V/110V) into high voltage for driving the magnetron which generates the microwave of a predetermined degree of high frequency. In such a situation, the microwave vibrates the water molecules in food, so that the food is cooked by friction heat produced due to the vibration of water molecules.
FIG. 1 is a partial cutaway perspective view of a general microwave oven. In FIG. 1, reference numeral 1 designates a body, 2 is a cooking chamber, 3 is a device chamber, 4 is a door, 5 is a rotational plate, and 6 designates a cover. The inner space of the body 1 is divided into a left and a right space in which a cooking chamber 2 and a device chamber 3 are respectively defined. Electric devices are installed in the device chamber 3. A cover 6 encases the body 1, thereby forming the appearance of the microwave oven. A door 4 is pivotally fixed to one side of the body 1, to open/close the front side of the cooking chamber 2. A rotational plate 5 is disposed at the bottom surface of the cooking chamber 2, and the food to be cooked is placed thereon. The rotational plate 5 is rotated by a driving motor (hereinafter referred to as DM; see FIG. 2) which is installed on the lower surface thereof. Additionally, reference numeral 7 designates a front panel, 8 is an air guide, 9 is a cooling fan, HVT is a High Voltage Transformer, HVC is a High Voltage Condenser, HVD is a High Voltage Diode, and MGT designates a Magnetron. Those are installed in the device chamber 3. The high voltage transformer HVT transforms the common voltage 220V/110V into high voltage 2000V. The high voltage 2000V is doubled to 4000V by the high voltage condenser HVC and the high voltage diode HVD. The magnetron MGT is driven by such doubled voltage 4000V to generate a microwave of 2450 MHz. The cooling fan 9 blows air into the device chamber 3 to cool the heated electric devices installed therein such as the magnetron MGT, high voltage transformer HVT, or the like. The air guide 8 is installed near the magnetron MGT, to guide air which has been heated while the magnetron MGT is cooled, into the cooking chamber 2. The front panel 7 is installed at the front surface of the device chamber 3. The user inputs the data of his selected keys into the microwave oven, and his selections for driving the microwave oven are displayed on the front panel 7.
FIG. 2 is a schematic block diagram of FIG. 1. In FIG. 2, reference numeral 10 designates a noise filter, 20 is a driving section, 30 is a microwave generator, 40 is a control section, 50 is a input section, and 60 designates a display section. An input section 50 inputs the signals of the user's selections into a control section 40. A plurality of function keys 51 are provided in the input section 50. Here, the function keys are for respective driving conditions of the microwave oven. More specifically, there could be the function keys for adjusting cooking temperature, cooking time, level of the microwave energy, or the like as the user wishes. In addition, there could be the function keys for selecting the automatic cooking process, in which the user inputs the data about the amount of the food so that the food is automatically cooked in accordance with the cooking data which were preset therefor. The display section 60 displays the driving conditions of the microwave oven. Here, the input section 50 and the display section 60 are preferably provided at the front panel 7 shown in FIG. 1. The driving section 20 comprises driving motors DM and FM for respectively driving the rotational plate 5 and the cooling fan 9. Further, the driving section 20 comprises relay switches RS1 and RS2, respectively for supplying the driving power to the high voltage transformer HVT and the driving motors DM and FM. Accordingly, when the relay switches RS1 and RS2 of the driving section 20 are turned on, the driving power is supplied to the high voltage transformer HVT and the driving motors DM and FM. A general microcomputer would serve as the control section 40. The control section 40 properly controls the driving conditions of the microwave oven by selectively turning on/off the relay switches RS1 and RS2 of the driving section 20. The control section 40 also sends the signals to the display section 60 and displays such driving conditions of the microwave oven. The high voltage transformer HVT transforms the common voltage supplied from the driving section 20 into high voltage, and transmits the high voltage to the microwave generator 30. The microwave generator 30 comprises the high voltage condenser HVC, the high voltage diode HVD, and the magnetron MGT. The microwave generator 30 is driven by high voltage supplied from the high voltage transformer HVT, just as it was described above with respect to FIG. 1. The noise filter 10 receives the driving power, and transmits the driving power to the driving section 20. Further, the noise filter 10 prevents feed back of high frequency wave generated from the microwave generator 30 toward an input line.
Operation of the conventional microwave oven constructed as above will be described below. First, the user pulls the door 4 of the body 1 and opens the cooling chamber 2. Then, the user places the food to be cooked on the upper surface of the rotational plate 5. Next, the user closes the door 4, and selects cooking conditions of microwave oven by selecting function keys 51 of the input section 50 which is provided at the front panel 7. By selecting the function keys 51, the user sets the cooking time, temperature, and level of the microwave energy as he guesses proper for the amount of the food placed in the microwave oven. In addition to such a manually-selected driving condition, there may be an automatically-selected driving condition in which the user simply selects keys provided for the food he/she is preparing and the amount thereof, so that the food is cooked in a manner which was preset in the microwave oven. Accordingly, the input section 50 inputs the signals from the selected keys to the control section 40, and the control section 40 drives the driving section 20 in accordance with the user's selections. More specifically, the control section 40 turns on the relay switch RS1 so that the power is supplied to the high voltage transformer HVT. Accordingly, the high voltage transformer HVT transforms the common voltage 220V/110V into high voltage. And the high voltage condenser HVC and the high voltage diode HVD double the high voltage to 4000V, and supply the same to the magnetron MGT. The magnetron MGT is driven by such doubled high voltage 4000V to generate the microwave of 2450 MHz. Then microwave is radiated into the cooking chamber 2 so that the food is cooked. Further, the control section 40 simultaneously turns on the relay switches RS1 and RS2 so that the control section 40 drives the driving motors DM and FM, respectively. Accordingly, the rotational plate 5 of the cooking chamber 2 is rotated so that the microwave is uniformly radiated to the food. In this situation, the cooling fan 9 of the device chamber 3 blows air into the device chamber 9, to cool the electric devices such as the high voltage transformer HVT, the magnetron MGT, the high voltage diode HVD, and the high voltage condenser HVC, etc. Here, the control section 40 turns on/off the relay switch RS1 regularly, to control the driving conditions of the magnetron MGT. Accordingly, the level of the microwave generated from the magnetron MGT are properly adjusted, so that the food in the cooking chamber 2 is appropriately cooked under the selected driving conditions.
Meanwhile, in addition to the manually-selected driving conditions, the conventional microwave oven further has an automatically-selected driving condition. With such an automatically-selected driving condition, however, the amount of the food can not be determined by the microwave oven. Accordingly, the user has to guess the best cooking mode for the food, and based on his/her guess, one selects corresponding function keys, and the microwave oven cooks the food in accordance with such inputted data. Here, when the food requires more time or greater level of microwave energy for cooking than the user inputted, the food is under-cooked. Likewise, when the food requires less time, or less level of microwave energy for cooking than the user inputted, the food is overcooked. Accordingly, in order to cook the food appropriately, it is important that the user may judge the exact amount of the food and drive the microwave oven accordingly.
The conventional microwave oven, however, can not offer the solution to the above-mentioned problem, since the user has to guess the amount of the food. Further, in the event that there is no function keys for the amount of the food the user wishes to cook, the user has to manually input the data for cooking time, level of microwave energy, etc., so that the preparation of the food becomes inconvenient and complex.
Further, when using a conventional microwave oven, since the user has to guess the amount of the food he/she is preparing, the preciseness of the food amount is not guaranteed, so that the cooking operation may be inappropriately performed. If the user selects an improper function key by his/her mistake or misjudgement, the food can be over-cooked, or under-cooked. Thus, the food can not be appropriately cooked.
There has been a solution suggested for the above-mentioned problem such as a gas sensor, a weight sensor, etc. which could be employed in a microwave oven to determine the amount of the food. However, since these devices are expensive and require a rather complex manufacturing process, the manufacturing cost is increased, and the efficiency is accordingly deteriorated.